A Cobalt Phosphine Complex in Five Oxidation States

Abstract

Here we report electrochemical, spectroscopic, and crystallographic characterization of a redox series of cobalt complexes in five sequential oxidation states. A simple bidentate phosphine ligand, cis-1,2-bis(diphenylphosphino)ethylene (dppv), allows for isolation of the 3+, 2+, 1+, 0, and 1− oxidation states of cobaltthe only known example of transition-metal complexes with redox-innocent ligands in five oxidation states. Electrochemistry of [Co(dppv) 2 ] 2+ reveals three reversible reductions and one reversible oxidation. Complexes in each oxidation state are characterized using single-crystal X-ray diffraction. The coordination number and geometry of the complex changes as a function of the oxidation state: including acetonitrile ligands, the Co 3+ complex is pseudo-octahedral, the Co 2+ complex is square-pyramidal, the Co + complex is pseudo-square-planar, and the Co 0 and Co − complexes approach pseudo-tetrahedral, illustrating structures predicted by crystal-field theory of inorganic transition-metal complexes.

Tuning Cobalt(II) Phosphine Complexes to be Axially Ambivalent

“…In our recent work on d 6 –d 10 cobalt complexes of dppv, we found that the d 7 Co II (dppv) 2 2+ core crystallizes with one axial ligand (acetonitrile), generating a pseudo-square pyramidal geometry which we previously reported ( 2 ) . Herein, we further report that the core also crystallizes with 0 or 2 axial ligands ( 1 and 3 ), and we provide the structural characterization of each of these complexes.…”

“…In our recent work on d 6 –d 10 cobalt complexes of dppv, we found that the d 7 Co II (dppv) 2 2+ core crystallizes with one axial ligand (acetonitrile), generating a pseudo-square pyramidal geometry which we previously reported ( 2 ). 11 Herein, we further report that the core also crystallizes with 0 or 2 axial ligands ( 1 and 3 ), and we provide the structural characterization of each of these complexes. The former is a structure of 4-coordinate divalent Co(dppv) 2 2+ in a rigidly planar geometry.…”

Incorporation of Switchable Inorganic Building Blocks into Heterometallic Coordination Polymers

“…Again this occurs at a more positive potential than that seen for the Co II /Co I in [Co­(terpy) 2 ] 2+ (Table ). The third reversible redox process is seen well below that, at E m = −1.79 V vs Fc/Fc + (Δ E = 0.11 V), and is associated with ligand reduction, which for [Co­(terpy) 2 ] 2+ occurs at about −2 V, whereas for the metal-free terpy ligand this occurs at about −2.5 V. …”

Two-Electron-Induced Reorganization of Cobalt Coordination and Metal–Ligand Cooperative Redox Shifting Co(I) Reactivity toward CO2 Reduction

“…Metal–ligand orbital interaction can increase the nucleophilicity of the metal center, , and the proton-coupled electron transfer lowers the potential energy. − Additionally, a ligand-dependent reorganization pattern of coordination structure may change a reaction path during electrochemistry. Hence, controlling the electron-transfer steps should be critical in determining the reaction paths and products. , In addition, given that an electrochemical reorganization occurs, a new CO 2 reactivity can be expected even in a metal complex without CO 2 reactivity.…”

“…Hence, controlling the electron-transfer steps should be critical in determining the reaction paths and products. 28,29 In addition, given that an electrochemical reorganization occurs, a new CO 2 reactivity can be expected even in a metal complex without CO 2 reactivity.…”